Experimental and clinical studies of using Nd: YAG laser via domestic metal cap and sapphire tip delivery systems

Sixteen segments of normal human cadaver aorta were irradiated by Nd: YAG laser beam delivered via domestic metal cap and sapphire tip fiber systems. Results revealed that the adherence to target tissue and tissue damage were more apparent with metal caps than those with sapphire tips. Furthermore, the latter had smoother edges of ablation crater less carbonization layers and smaller thermal necrotic zones. The delivery systems were used to perform laser angioplasty in 2 iliac and 5 coronary atherosclerotic arteries and all achieved immediate recanalization.     

Effect of laser irradiation on atherosclerosis vascular segments in relation to wave length and pulse width

The interaction of pulsed Nd:YAG laser radiation and atherosclerotic vessel wall is reported. The effects in the area of radiation were examined at an infrared, green, and ultraviolet wavelength at variable pulsewidths. The laser beam was focused directly on the plane surface of the tissue. The macroscopic and histologic examinations demonstrate that thermal damage of tissue is higher at an infrared wavelength than at a green wavelength and respectively at an ultraviolet wavelength. With increasing pulsewidth an increase of coagulation and necrosis of plaque material and adjacent vessel wall can be noted. The results show that for the precise ablation of plaque without adjacent vessel wall injury short pulsed ultraviolet radiation is preferable.     

The development of laser angioplasty

Recent developments in technology have stimulated interest in the use of catheter-directed laser energy for removal of atherosclerotic plaques. Over the past three years, intensive research efforts by a number of investigators have defined the potential therapeutic benefit of laser angioplasty, as well as its limitations. Unlike balloon angioplasty, the laser has the capacity to remove totally atheromatous plaque or thrombus by photovaporization. Unique properties of the laser allow light energy to be concentrated for plaque removal. Arterial damage adjacent to the plaque is prevented by certain lasers, while others produce thermal injury to the arterial wall. Chemical pretreatment with vital dyes or drugs has been shown to enhance absorption of laser radiation by plaque and may enable selective destruction of the arterial plaque. Fiberoptic catheters have been designed to transmit laser energy to remote intravascular targets; however, precise guidance systems for catheter delivery have not been developed sufficiently for safe intracoronary application. Complete arterial healing by endothelial cell migration has been demonstrated after laser ablation of plaque in animal studies. Among the first four clinical trials of laser angioplasty, relief of atherosclerotic obstruction was successful using argon, neodymium-YAG, and carbon dioxide lasers. Despite the satisfactory initial appearance of laser-treated arteries, the long-term effects and risk of atherogenesis are undetermined. A potential risk of thrombosis has been identified after laser application, especially with the argon and NdYAG lasers. Further basic and clinical research are needed to establish the role of this promising new technology in the treatment of cardiovascular disease.     

Laser ablation of human atherosclerotic plaque without adjacent tissue injury

Seventy samples of human cadaver atherosclerotic aorta were irradiated in vitro using a 308 nm xenon chloride excimer laser. Energy per pulse, pulse duration and frequency were varied. For comparison, 60 segments were also irradiated with an argon ion and an Nd:YAG (neodymium:yttrium aluminum garnet) laser operated in the continuous mode. Tissue was fixed in formalin, sectioned and examined microscopically. The Nd:YAG and argon ion-irradiated tissue exhibited a central crater with irregular edges and concentric zones of thermal and blast injury. In contrast, the excimer laser-irradiated tissue had narrow deep incisions with minimal or no thermal injury. These preliminary experiments indicate that the excimer laser vaporizes tissue in a manner different from that of the continuous wave Nd:YAG or argon ion laser. The sharp incision margins and minimal damage to adjacent normal tissue suggest that the excimer laser is more desirable for general surgical and intravascular uses than are the conventionally used medical lasers.     

Thermal Effects In Vivo from Holmium: YAG Lasing in the Intracoronary Setting

While the thermal effect of laser energy does ablate atheromatous plaque, thermal injury to adjacent tissue produces high rates of arterial thrombosis and spasm. Holmium:YAG lasers use a pulsed laser source to maximize photoblative effects while minimizing thermal effects. These lasers have been utilized clinically to ablate thousands of complex coronary lesions with low rates of spasm and thrombosis, suggesting that little or no thermal injury occurs with these devices. However, we have been able to detect thermal injury in patients angioscopically in coronary arteries after holmium:YAG lasing. Here we report the use of directional coronary atherectomy (DCA) to òbiopsyó arteries in patients following holmium:YAG laser treatment, allowing direct histologic examination of lased tissue. Thirty such lased DCA samples were matched for patient age, gender, target vessel, and lesion characteristics with thirty control DCA samples obtained from patients undergoing DCA without prior lasing. Blinded pathologic examination correctly identified 27/30 control samples but only 18/30 lased samples. Subsequent unblinded analysis, sometimes with recutting and restaining of tissue blocks, resulted in the detection of thermal effects in 27/30 lased samples. The thermal effects seen included edge disruption, charring, coagulation necrosis, and most commonly, vacuolization. We conclude that holmium:YAG lasing does produce detectable thermal effects in tissue in most patients. These effects can be quite subtle or can be extensive, but do not predict poor patient outcome.     

Plaque ablation by excimer laser irradiation using a movable energy-transmitting device

During the past 2 years, excimer laser energy has been shown to provide a highly suitable type of atherosclerotic plaque ablation, especially in small-diameter vessels such as coronary or crural arteries. Nevertheless, transmission of far-ultraviolet pulsed laser power has remained a major problem in animal studies and clinical trials. In an attempt to solve this problem, we constructed an energy-transmitting device for use with a Lambdaphysics EMG 102 excimer laser. The transmission system, which was housed in a rigid articulated arm, allowed movement in all directions and rotation along the long axis, thus permitting easy handling and guiding of the laser beam in the operating field. To test whether this device could deliver enough energy to remove atherosclerotic plaques within a period that would meet the requirements for intraoperative use, we obtained fresh human cadaver coronary arteries both with and without atherosclerotic disease, and irradiated them vertically and coaxially. A power meter was used to determine the effective amount of energy delivered at the distal end of each vessel. Energy densities up to 3 J/cm(2)/pulse were obtained, owing to energy focussing within the transmitting device. At 5 Hertz (Hz), tissue ablation consisted of approximately 20 microm/pulse. Areas of normal vascular tissue, as well as fibrohyalinous and lipid plaque components, were promptly ablated. Macroscopically, the "lasered holes" appeared well-circumscribed, with clear-cut surfaces and no carbonization. Light microscopy revealed no thermal damage to the boundary tissue. With this new energy-transmitting device, the surgeon can use excimer laser irradiation intraoperatively. There is no significant loss of energy between the generator and the tip, and energy densities of 3 J/cm(2)/pulse are available for sufficient plaque removal.     

Holmium YAG laser coronary angioplasty with multifiber catheters

Excimer lasers are being extensively used for coronary angioplasty along with multifiber over-the-wire catheters. To determine whether another wavelength could be an alternative, the laser-tissue interaction and the clinical usefulness of an infrared laser were studied. The laser consisted of a Holmium YAG pulsed laser coupled into a multifiber catheter. Experimental data from our laboratory showed that this solid state laser had the ability to cut calcified tissue, to be preferentially absorbed by atheroma, and to ablate tissue even when the catheter tip was positioned at a distance from the target. These results were obtained with only minimal thermal effects. After assessment of the efficacy and safety of this technique, laser angioplasty was performed in 53 consecutive patients with totally occluded (40%) or stenosed (mean percent 94) coronary arteries with a mean length of 6 mm. The primary laser and the procedure success rate were 64% and 94%, respectively. Failures were due to inability to advance the catheter against the lesion or to cross the obstruction. Stand-alone laser therapy could be achieved in only 18% of patients. In previous dilatation failures, laser irradiation allowed for subsequent balloon angioplasty to be successfully performed at a lower inflation pressure than that used in the failed dilatation. Complications included abrupt (during the procedure) and early (within 24 hours) vessel closure in 19% of cases, dissection without hemodynamic consequence in 28% and spasm. Reoccluded arteries could all be recanalized with dilatation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histological and angiographic effects of a pulsed holmium:YAG laser in normal and atherosclerotic human coronary arteries and aorta.

OBJECTIVE: The aims were (1) To determine the histological and angiographic effects of holmium:YAG laser energy delivered through clinical multifibre laser catheters on fresh cadaveric coronary arteries; and (2) to relate the placement of optical fibres in the catheter to patterns of tissue ablation in cadaveric aorta. METHODS: Eight fresh cadaveric hearts and segments of aorta were used. Hearts were mounted on a new pressure perfusion device. The laser catheter was delivered over a guidewire in the lumen until it met an area of resistance. The coronary artery lumen was perfused at approximately 100 mm Hg mean pressure. These arterial areas were identified on angiography, marked, and then exposed to laser energy in the range 600-3000 mJ.mm-2. Normal and atherosclerotic areas of fresh cadaveric aortic strips were exposed to increasing laser energies using either constant or increasing fluence. Coronary arteries were pressure perfused with formalin for 18-24 h at 100 mm Hg mean pressure, and aortic strips were immersed in 5% formalin. Light and scanning electron microscopy studies were carried out. RESULTS: There were no perforations or dissections by angiography in the fresh coronary arteries. One of 15 normal coronary artery segments and 10 of 16 of the pressure perfused, fixed, atherosclerotic coronary artery segments showed thermal changes associated with atherosclerotic plaque ablation. In aortic tissue, thermal effects extended 0 to 0.6 mm lateral to the ablated crater. Acoustic effects were seen only in the aortic strips after ablation at fluences > 1000 mJ.mm-2. The "dead spaces" around the optical fibres in the catheter resulted in significant amounts of coagulated tissue fragments remaining in the crater. CONCLUSIONS: Holmium:YAG laser energy delivered through multifibre catheters ablated atherosclerotic tissue in coronary arteries with minimal damage to the normal walls. The cadaveric coronary artery perfusion apparatus is useful for assessing catheter delivery and mobility and the effects of laser energy on the coaxially orientated normal and atherosclerotic coronary arterial wall.     

Low-Power Contact Nd: YAG Laser Endoscopy

Abstract: Laser application in gastrointestinal endoscopy started with the development of flexible optical fibers in about 1970. Originally, non-contact irradiation with high power Nd: YAG lasers of 100 watts (W) was used for gastrointestinal hemostasis. It was difficult to achieve safe and reliable irradiation with this method, the quarts fiber tips were susceptible to coagulation damage, and the cost was high. As a result local injections were recognized as an inexpensive and excellent method of producing hemostasis, and became the treatment of first choice. Therefore, the endoscopic use of lasers shifted from hemostasis to the topical treatment of tumors. In 1984 low-power Nd: YAG laser irradiation at 1 to 30W became possible using a ceramic contact probe co-developed by the authors and the Surgical Laser Technology Japan Co. This made photocoagulation, vaporization, cutting and local hyperthermia (Laserthermia) feasible. Improvements in laser irradiation efficiency led to the development of inexpensive equipment, costing less than one-third of the price of conventional equipment. The application of low-power contact lasers significantly improved the clinical efficacy of the treatment of minute cancers, but the technique has the same limitations as other endoscopic methods. Furthermore, because laserthermia is still being developed, the best technique has not yet been fully defined. In the future, treatments that can be used effectively in association with low-power contact laser therapy need to be identified. Low-power contact laserthermia, local hyperthermia with microwaves, and photodynamic therapy with excimer dye lasers all need to be studied further. This will contribute to the development of a minimum invasive therapy for gastrointestinal lesions.     

Angioplasty of coronary arteries by laser radiation in 1988

The ability of laser radiation to destroy healthy or pathologic vascular tissue in vitro and in vivo marked the beginning of therapeutic ablation of atheromatous deposits in man. The problems encountered by application of this procedure to treatment of coronary heart disease are very complex, and experience acquired using lasers for peripheral vascular disease is of not much help in this area. It is clear that continuous emission lasers (YAG, Argon, CO2), which produce coagulation necrosis, thrombosis, and vasospasm must be ruled out in favor of impulse type lasers (CO2TEA, YAG Q-S, pumped lasers with dye and exciplex lasers) if the latter can provide a critical thermal relaxation time. Currently, exciplex lasers are a possible method whose potential efficacy and safety gave been demonstrated with certainty in coronary angioplasty. Indeed, although their mechanism of action is poorly understood, they offer the twofold advantage of being able to focus on a volumetrically defined ablation, and to leave the surrounding tissue intact. The clinical application of these tools remains to be developed. Laser angioplasty requires in situ diagnostic methods based on the optical utilization of intrinsic and extrinsic chromophores, the objective of intensive research. Its relative role in comparison to other methods of ablation, and specific indications remain to be defined.     

Role of laser and thermal ablation devices in the treatment of vascular diseases

Since the first coronary angioplasty in 1977, both the number and complexity of interventional procedures have grown dramatically. Continuous-wave and pulsed lasers may further extend the capabilities of balloon angioplasty. Fiberoptic catheters may be used to transmit continuous-wave laser energy to ablate plaque via thermal mechanisms. Pulsed laser systems (such as the excimer) are technologically more complex than the continuous-wave systems, but may prove superior in small vessels given their ability to ablate plaque with minimal associated effects. On the other hand, modifications of the fiber-optic tip, such as the placement of a metal cap, have yielded even better results than current bare fiber systems. Such laser thermal techniques have proved a useful adjunct to balloon dilatation in peripheral vessels, but further research is necessary to determine their effect on coronary arteries. New, nonlaser technologies, however, may provide simpler power sources for thermal angioplasty. Although balloon angioplasty remains the cornerstone of interventional vascular therapy, new technologies should help to further expand the indications for nonsurgical interventions.     

Argon vs. neodymium YAG laser photocoagulation of experimental canine gastric ulcers

A neodymium YAG (Nd:YAG) laser was evaluated in a dog ulcer model used in the same manner as is recommended for bleeding patients (power 55 W, divergence angle 4 degrees, with CO2 gas-jet assistance). The experiments were performed during sterile laparotomy in heparinized dogs. Bleeding gastric ulcers were photocoagulated until bleeding stopped and then examined histologically 7 days later when depth of tissue injury was maximal. In the first series of experiments, the Nd:YAG laser was compared with the 7-W argon laser in the same dogs. Both lasers stopped bleeding from all experimental ulcers. The 55-W Nd:YAG laser caused full-thickness injury to the gastric wall beneath 11 of the 14 treated ulcers, whereas the 7-W argon laser caused no full-thickness injury beneath 14 treated ulcers. In a second series of experiments, we tried to determine whether varying exposure times with the 55-W Nd:YAG laser would make it less injurious; it did not. In a third series of experiments, the 55-W Nd:YAG laser was tested with and without CO2 gas-jet assistance in order to determine if this would affect the depth of injury; it did not. In the final series of experiments, the wattage of the Nd:YAG laser was varied to see if this would reduce depth of injury; lower wattage did not stop bleeding, and intermediate and higher wattages did stop bleeding but did not reduce depth of injury. We conclude that the 55-W Nd:YAG laser as it is currently used clinically produces deeper tissue damage than the argon laser in our animal model. This damage is not reduced by changes in power, duration of exposure, or the presence of gas-jet assistance.     

The qualitative effects of laser irradiation on human arteriosclerotic disease

To determine the effects of laser irradiation upon human coronary atherosclerotic disease, coronary plaques were extracted from fresh human cadaver hearts. Seventy-four diseased artery samples were sectioned either transversely or longitudinally and subjected to laser treatment from argon-ion and carbon dioxide sources. The laser beam affected vaporization and patency in fibrous, lipoid, and calcified plaques as observed histologically. Calcified blockage showed greater extent of charred remnants following controlled thermal injury than did fibrous or lipoid obstructions. The area and depth of penetration varied directly with intensity and duration of photoirradiation and inversely with the density of the atherosclerotic tissue. This study supports further research work on the use of lasers to effect relief of atherosclerotic obstructions.     

Applicability of laser to assist coronary balloon angioplasty

Severe atherosclerotic obstructed coronary artery disease (CAD) may preclude passage of a balloon catheter for transluminal coronary angioplasty (TCA). Since lasers have been shown to effectively vaporize CAD plaque, the initial application of laser to effect a lumen large enough to accommodate the angioplasty catheter for further dilatation was explored. Eleven postmortem human CAD segments which did not permit passage of a 1.33 mm shaft diameter angioplasty catheter were studied. Argon laser radiation (14 to 90 J) transmitted via 400 micron core diameter quartz fiber onto the stenotic channel of 0.58 mm created a vaporized lumen of 1.77 mm (mean increase of 1.31 +/- 0.25 mm, p less than 0.001). The laser procedure allowed the balloon angioplasty catheter to be pushed into the stenosis. TCA was then performed (7 atm, 45 seconds) and expanded the channel to 2.12 mm (additional mean increase of 0.38 +/- 0.07 mm, p less than 0.001). In terms of percent luminal narrowing, laser radiation reduced obstruction from 80% to 45% (mean difference of -38.7 +/- 4.6%, p less than 0.001), and TCA caused a further decrease to 37% (mean difference of -9.3 +/- 1.9%, p less than 0.001). Thus, in tight atherosclerotic lesions, the laser may be useful in creating an initial opening enabling the placement of the balloon angioplasty catheter which, in turn, can further dilate the lased stenotic coronary lumen.     

Percutaneous coronary laser angioplasty in a patient with chronic total obstruction of the right coronary artery

Percutaneous coronary laser angioplasty was performed in one patient with total occlusion of right coronary artery without further balloon angioplasty in the ablated site. First of all, we used intracoronary urokinase in a total amount of 60,000 units that resulted in opening the total occluded right coronary artery to provide a passage of guidewire of laser catheter. Then a laser catheter was inserted through the guide catheter and its metal cap was in contact with the atherosclerotic lesion. The Nd:YAG laser was activated to vaporize the lesion (total energies of 54 J). Finally, the degree of residual stenosis was reduced from 95% to 20%. Percutaneous coronary laser angioplasty is a new method in treating coronary artery disease, yet it is still in its infant stage and further work is needed to develop this technological procedure.     

Identification of photoproducts liberated by in vitro argon laser irradiation of atherosclerotic plaque, calcified cardiac valves and myocardium

To determine how laser light effects alterations in cardiovascular tissue, photoproducts liberated as the result of argon laser irradiation of atherosclerotic plaque, myocardium and calcified aortic valve leaflets were analyzed by gas chromatography, gas chromatography-mass spectrometry and absorbance spectroscopy. The products formed in gas phase are those expected when proteins and porphyrins are pyrolyzed--light hydrocarbon fragments, carbon monoxide and water vapor. The laser-generated products dissolved in solution are those expected when a protein chain or porphyrin ring is degraded in a thermal reaction, namely protein fragments and nitrogen heterocyclic ring fragments. These photoproducts are those typical of combustion or thermal degradation, and indicate that the fundamental nature of laser irradiation of coronary plaque, myocardium and calcified valve leaflets is thermal rather than photochemical. Thermal degradation of myocardium is more extensive than thermal degradation of atherosclerotic arteries or calcified valves because the red hue of myoglobin-containing myocardium enhances the absorption of the blue-green argon laser light. In contrast, the yellow-white hue of both atherosclerotic plaque and calcified aortic valve leaflets allows less complete absorbance of the argon laser light, leading to a lesser amount of converted heat and, therefore, less complete thermal degradation.     

Palliative laser therapy for tumours of the gastrointestinal tract.

The argon ion and Nd: YAG lasers were used initially in the mid 1970s to produce haemostasis in acutely bleeding peptic ulcers. With the evolution of treatment techniques, the main area of use of the Nd: YAG laser has now become the palliation of upper and lower GI malignancies. Thermal ablation of tumours may be achieved endoscopically by non-contact laser application at high power, or in the contact mode using artificial sapphire probes at much lower energy levels. Still lower powers can be employed therapeutically using interstitial hyperthermia, and this is best applied endoscopically to exophytic tumour nodules in the gut lumen or to tumours localized ultrasonically in solid organs, such as the liver or pancreas. PDT involves destruction of previously photosensitized tumours by the cytotoxic action of singlet oxygen released on exposure of the neoplastic tissue to light of an appropriate wavelength. Although the theory is attractive, the available experimental and clinical information suggests that treatment should, for the present, be confined to small or early malignancies whose depth of invasion can be verified by endoscopic ultrasound or other imaging techniques. PDT carries the biological advantage of healing by regeneration with preservation of connective tissue stroma, while the Nd: YAG laser causes destruction by thermal coagulation or vaporization and subsequent healing by fibrosis. Laser therapy of GI tumours expands the range of therapeutic endoscopic procedures in a relatively safe and readily repeatable manner which achieves high patient tolerance. By reducing morbidity, mortality and time spent in hospital, it offers significant advantages in the palliative treatment of conditions previously managed by conventional surgery, and also offers opportunities for treatment of previously inoperable disorders. Developments in laser technology and diagnostic imaging techniques are likely to promote laser therapy in the future as a primary treatment modality.     

Experimental intracoronary Excimer laser angioplasty

To determine the feasibility of intracoronary application of pulsed ultraviolet laser light 38 coronary arteries of 18 in situ hearts were treated with the bare fiber technique and a specially constructed catheter device. Eight hearts had no coronary artery disease, in 10 hearts coronary artery disease of one or more vessels could be documented angiographically. Total time of laser irradiation varied from 30-490 seconds. Radiation was performed until vessel wall perforation was documented. In all cases a reduction of the stenotic area was realized using the bare fiber technique. Due to a lack in the flexibility of the bare fiber only proximal lesions could be treated and the time of perforation could not be precisely predicted. Dissections were observed in six coronary arteries. The handling of the catheter device was comparable to the conventionally used balloon technique. Ablative treatment of distal vessel lesions was possible. Perforations did not occur. The histologic specimens documented smooth lumen margins not revealing thermal damage. It can be expected that the innovative catheter device will enhance the intracoronary use of pulsed laser light.     

The excimer laser: gross, light microscopic and ultrastructural analysis of potential advantages for use in laser therapy of cardiovascular disease

Excimer lasers are pulsed gas lasers that use a mixture of a rare gas and halogen as the active medium to generate pulses of short wavelength, high energy ultraviolet light. A krypton-fluoride gas mixture was used to achieve an excimer emission at a wavelength of 248 nm. A total of 30 atherosclerotic coronary artery segments were irradiated over a range of pulse energies (250 to 750 mJ), repetition rates (2 to 25 Hz), average powers (1.9 to 18.8 watts) and cumulative exposures (3 to 12 seconds). In no case was there gross, light microscopic or ultrastructural evidence of the pathologic injury typically associated with continuous wave laser irradiation of coronary artery segments. Similar results were achieved after excimer laser irradiation of 30 samples of myocardium. Excimer irradiation of calcified aortic valve leaflets accomplished focal debridement without pathologic tissue injury; when total debridement was attempted, however, gross charring was observed. The paucity of pathologic alterations observed after excimer irradiation of cardiovascular tissue may prove beneficial in precisely controlling laser ablation of pathologic tissue without injury to the surrounding normal tissue. Clinical application of excimer laser irradiation requires resolution of several issues, including the development of suitable fiber optics and laser coupling, evaluation of potential ultraviolet toxicity, and demonstration that ultraviolet light can be transmitted through a blood-filled system.     

Pulsed laser and thermal ablation of atherosclerotic plaque: morphometrically defined surface thrombogenicity in studies using an annular perfusion chamber.

Although clinical trials using laser and thermal angioplasty devices have been underway, the effects of pulsed laser and thermal ablation of atherosclerotic plaque on surface thrombogenicity are poorly understood. This study examined the changes in platelet adherence and thrombus formation on freshly harvested atherosclerotic aorta segments from Watanabe-heritable hyperlipidemic rabbits after ablation by two pulsed laser sources (308-nm xenon chloride excimer and 2,940-nm erbium:yttrium-aluminum-garnet [YAG] lasers) and a prototype catalytic hot-tip catheter. Specimens were placed in a modified Baumgartner annular chamber and perfused with citrated whole human blood, followed by quantitative morphometric analysis to determine the percent surface coverage by adherent platelets and thrombi in the treated and contiguous control areas. Pulsed excimer laser ablation of plaque did not change platelet adherence or thrombus formation in the treated versus control zones. However, photothermal plaque ablation with a pulsed erbium:YAG laser resulted in a 67% reduction in platelet adherence, compared with levels in control areas (from 16.7 +/- 2.2% to 5.5 +/- 1.8%; p less than 0.005). Similarly, after plaque ablation using a catalytic thermal angioplasty device, there was a 74% reduction in platelet adherence (from 29.2 +/- 5.1% to 7.7 +/- 1.6%; p less than 0.005) and a virtual absence of platelet thrombi (from 8.6 +/- 2.3% to 0.03 +/- 0.03%; p less than 0.005). This reduced surface thrombogenicity after plaque ablation with either an erbium:YAG laser or a catalytic hot-tip catheter suggests that thermal modifications in the arterial surface ultrastructure or thermal denaturation of surface proteins, or both, may be responsible for reduced platelet adherence. These in vitro findings indicate that controlled thermal plaque ablation by catheter-based techniques may elicit endovascular responses that can reduce early thrombus formation during angioplasty procedures.